The use of Bacillus anthracis as a bioweapon depends on dispersal of its spores in the environment, entrance into the body, spore uptake by the human host cells, germination of the spores in the host and the pathological consequences of the host response to the toxins elaborated by the vegetative cells within the host. Very little is known of the mechanisms of spore entry into the host, including the nature of targeted cell types in the airways, digestive tract and skin, and their subsequent initial encounter with cellular and humoral elements of the innate and adaptive immune response. An understanding of these host-spore interactions and the very early immune responses to the spores as they initiate the germination process will likely permit the development of an interventional vaccine or drug strategy that would act prior to the germination of spores and outgrowth of the vegetative form within the host and thus prevent development of Anthrax. We have identified mouse cell types involved in initial B. anthracis spore contact and will now analyze signaling pathways activated after spore entry and ingestion. We will define host cell receptors and spore-ligands involved in spore uptake and induction of intracellular activation pathways that affect intracellular spore survival. Multiple gene- targeted mice will be used to identify these pathways which promote or block spore killing bi phagocytic cells. We will test the effects of anti-spore antibodies on the fate of spores in vivo. These goals will be achieved by a combination of flow cytometric analysis and biochemical analysis using in vitro cells lines and primary phagocytes. If we can induce passive protective immunity with antibodies, we will attempt to elicit similar vaccine-induced immune responses and test the effects of these in long-term memory responses and determine the intracellular fate of spores if they are opsonized with antibodies to different spore targets. By identifying the spore-associated target molecules of these antibodies, we will be able to identify potential mechanisms to rapidly inactivate spores prior to establishment of infectious loci and vegetative cell outgrowth resulting in death from toxemia and septicemia. Therapeutic strategies of this nature would be a major supplement to the current PA-based vaccines as well as to the current recommended antibiotic regimens and in the case of multi-resistant B. anthracis strains engineered to produce additional toxins. Public Health Relevance: Bacillus anthracis spore dispersal as an agent of terrorism remains as an important issue to both civilian and military personnel. The exosporium, being the outermost layer of the spore stage of this organism, is the first point of contact of spores with host cells. By defining the molecules on the surface of spores and the receptors on host cells we may be able to develop interventional strategies to induce immune protection or drugs that will inactivate or destroy spores thus preventing bacterial development, the elaboration of toxins, and death.